Safety and penetration resistant laminates having thermoplastic and/or glass laminae are usually bonded together by adhesive interlayers of a polymeric material. Unlike the structural laminae, the interlayer material is highly elastomeric to provide better adhesion and relieve stresses in the laminate.
As criteria for selection, the interlayer material must have: (1) a high impact energy absorption level so that it may withstand high impact from moving objects, high tensile strength and high percentage of elongation are measures of this property; (2) good shear and tear strength to prevent rupture from the broken laminae; (3) good adhesion to the laminae so as to bond the laminate and to prevent broken pieces of the laminate from flying and causing injury; (4) good optical transparency; and (5) good weathering characteristics.
Although various primers have been used to increase adhesion, the interlayer materials to date have been self adhesive, that is the interlayer is an adhesive material which also possesses the above criteria. U.S. Pat. No. 3,666,614 discloses interlayer materials in which the adhesive properties are activated by the use of heat and pressure. U.K. Pat. No. 2,015,427 discloses interlayer materials wherein the adhesive properties are activated by the use of UV radiation.
While the interlayer materials disclosed by the above patents have worked well, it is very difficult to obtain the optimum combination of the above given criteria. A material which exhibits desirable adhesion may be lacking in shear and tear strength or high impact energy absorption. Fashioning an interlayer material with an optimum level in each area of the above criteria is a widely recognized problem in the art.
Further, the interlayer materials disclosed above require much capital investment and many man hours in constructing laminates which contain them. For example, the great majority of safety and penetration resistant laminates are laid-up and bonded using interlayer materials in which the adhesive properties are activated by heat and pressure.
Heat and pressure bonding is conducted in batches usually at temperatures ranging from about 80.degree. C. to 205.degree. C and preferably from about 110.degree. C to about 140.degree. C; and at pressures of from about 2 to 300 p.s.i., and preferably at pressures of from about 150 to about 250 p.s.i. The bonding is conducted in autoclaves, hydraulic presses, and similar devices. It is recognized in the art that such methods are cumbersome and result in laminates containing residual stress especially where diverse laminae are bonded.
Thus, interlayers in use today suffer from two recognized drawbacks: the difficulty of obtaining all essential physical properties at their optimum level in a homogeneous interlayer material and the cumbersome process of activating the adhesive characteristics of the interlayer material.
Therefore, it is an object of the present invention to provide a laminate containing a composite interlayer with the various constituents of the composite interlayer directed towards providing various necessary physical properties.
It is another object of the present invention to provide a laminate containing a composite interlayer including a thermoplastic sheet bonded on two faces with a contact or pressure sensitive adhesive.
It is another object of the present invention to provide a laminate containing a composite interlayer including a polycarbonate ply bonded on two faces with a contact or pressure sensitive adhesive.
It is yet another object of the present invention to provide a laminate containing a composite interlayer material which avoids the use of cumbersome processes in the bonding of laminates.